This invention relates to a surgical aid and a method for employing same. The surgical aid of the invention is particularly useful in connective tissue grafting procedures, such as ligament grafting as may be utilised in the surgical reconstruction of a joint.
Connective tissue surgery can involve certain difficulties which are not experienced in other surgical procedures, in view of the significant tension which is often required to be endured by the connective tissue after surgery. For example, in the surgical reconstruction of the anterior cruciate ligament of a human knee, often a tissue graft is taken from healthy connective tissue and affixed in place of the damaged ligament. Because of the relatively high tensive load bearing requirements of the connective tissues in the knee joint, it is vitally important that the ends of the tissue graft attach securely at the bone insertion points. It is therefore desirable to enhance the fixation of the graft at each end thereof.
Depending upon the particular surgical procedure employed, a connective tissue graft may be required to be passed through bores which have been drilled in bone structures. The drilled bores are preferably as close in diameter as possible to the size of the end portions of the graft where the graft ends are to be attached therein. Thus, sometimes considerable force may be required in order to draw the tissue graft through the hole in order to overcome the frictional forces acting between the graft and aperture surface. In previous surgical techniques it has been known to attach a suture to the end of the tissue graft for the purpose of drawing the graft through the aperture, but the suture can sometimes tear the graft tissue if pulled too hard. In the worst case the tissue graft may be ruined, with the result of serious consequences for the graft recipient. Further tension may be required to be applied to the graft during the surgical procedure in some instances where it is desirable for the graft to be under tension when surgically attached.
Another technique has been proposed in U.S. Pat. No. 5,456,721 (Legrand). In that proposal, a tendon is located within a resorbable yarn. In a first embodiment the ends of the sheath are formed with loops which are engaged by a U-shaped member which is used to interconnect the loops with the graft and bone tissue. In another technique, the sheath is located within an insertion tube, the head of which forms an anchoring device for one end of the graft. The present invention utilises a bioabsorbable sheath but the sheath has different properties so that it can be used in novel and advantageous ways.
The object of the present invention is to provide a novel sheath for use in ligament grafting, the sheath having elongate pliable ends to facilitate insertion and positioning of the graft.
Another object of the present invention is to provide a novel device for assisting in ligament grafting.
Another object of the present invention is to provide a method of facilitating placement of a ligament graft utilising a sheath having elongate end portions which can be pulled to facilitate placement and positioning of the graft.
A further object of the invention is to provide a novel ligament graft assembly which includes a sheath having elongate end portions which facilitate insertion and placement of the graft.
According to the present invention there is provided a sheath for use in ligament grafting, said sheath being formed from or including bioabsorbable material and having a relaxed state in which the sheath has a diameter in the range about 8 mm to about 15 mm and a stretched state in which the length of the sheath is at least five times its length in its relaxed state.
Preferably the length of the sheath in the stretched state is about ten times the length in its relaxed state.
Preferably the diameter of the sheath in its stretched state is about 0.1 to 0.25 of the diameter in the relaxed state.
Preferably the diameter of the sheath in its relaxed state is in the range 1.5 to 2.5 mm.
The invention also provides a device for assisting in ligament grafting comprising:
a holder having a hollow body which is open at both ends for receiving, in use, a ligament graft;
a sheath mounted over the hollow body;
said sheath being formed from or including bioabsorbable material and having an expanded diameter state in which engages the hollow body and a reduced diameter state in which its length is substantially greater than its length in the expanded diameter state, the arrangement being such that, in use, a ligament graft can be located within the hollow body and a one end of the sheath pulled from one end of the hollow body so that a first end of the graft is withdrawn from the body and retained in the sheath so the body can then be removed from the other end of the sheath whereby a ligament graft assembly is formed in which the graft is located in an intermediate portion of the sheath in its reduced diameter state.
The invention also provides a method of facilitating placement of a ligament graft comprising the steps of forming a ligament graft assembly by placing a ligament graft within a sheath whilst the sheath is in an expanded diameter state and pulling respective ends of the sheath away from the graft so that the graft remains enveloped by an intermediate portion of the sheath, the end portions of the sheath being elongate and in a reduced diameter state, forming first and second holes in first and second bones, pulling one of said end portions through said holes so that the graft is carried with the sleeve until one end of the graft is located in the first hole and the other end of the graft is located in the second hole.
The invention also provides a ligament graft assembly comprising a ligament graft and a sleeve formed from bioabsorbable material, the graft being located within an intermediate portion of the sleeve and end portions of the sleeve being elongate and cord like to enable placement ends of the graft at a respective graft site by pulling one or both of said end portions of the sheath.
Preferably, the sheath is formed from strands of bioabsorbable material having a thickness in the range 0.06 to 0.55 mm and preferably about 0.175 mm.
Preferably further, the material is formed as an open mesh fabric, the mesh size of which is 2.5 to 3.5 mm (as measured when the sheath is flat and relaxed).
Preferably further, the sheath has substantial linear expansion, preferably in the range from 10 to 20 times. For instance, if a length of the sheath material in a relaxed state is say 30 mm in length (and having a diameter of the order of say 20 mm), it can be stretched to form a string or cord like structure having a length say of about 300 mm. This enables the graft to be located in a central part of the sheath which is partly expanded and the end parts of the sheath to serve as strings or cords for use in insertion and placement of the graft.
The invention also provides a sheath for a connective tissue graft comprising a mesh of bioabsorbable strands in the form of a tube which is collapsable about its axis to ensheath a connective tissue graft inserted therein to allow axial tension applied to the sheath to be at least partially transmitted to the graft.
The sheath is preferably braided from a plurality of strands of thread or yarn. Alternatively, the sheath may be woven or knitted to form the tube structure, also preferably from a plurality of strands. The weave or knit pattern is preferably locked so that the sheath does not lose its integrity by running or the like if some of the strands are broken.
The strands forming the sheath may all be constructed from a bioabsorbable material, although it is also possible for only a proportion of the strands to be bioabsorbable and the remaining strands constructed from non-absorbable biocompatible materials. Some suitable bioabsorbable materials include polyglycolic acid (PGA) and polylactic acid (PLA) materials formed into fibres. Poliglecaprone and polydioxanone materials can also be utilised.
In one particular form of the invention, the sheath is formed from 24 strands of suture material, each 4/O polyglycolic acid, interwoven into a tubular structure having a relaxed circumference of about 2 centimeters.
The mesh sheath of preferred embodiments of the invention may additionally provide a framework for the impregnation of growth enhancing factors, cultured cells or other pharmacological agents, to aid in improved recovery from the graft surgery.
In use of the sheath for connective tissue graft surgery, the graft would typically be inserted into a section of the sheath material which is of a length so as to be somewhat longer than the graft itself. The ends of the sheath may then be pulled to apply tension to the sheath to facilitate the desired collapsing contraction of the sheath about the outside of the graft.
With the graft ensheathed by the mesh, a component of axial tension applied to the sheath is transmitted to the graft itself. The graft may then be attached into its site of application with the sheath in place, and end portions of the sheath material trimmed away. Preferably the fixing means applied to the graft also fixes the sheath in place. For example where interference screws are used for attachment of the graft ends, the screws may be inserted through the sheath mesh, which can aid in fixation of the graft in the short term at least.
In accordance with another aspect of the invention, there is provided a method of connective tissue grafting comprising inserting a tissue graft into a length of sheath constructed as described broadly above, applying axial tension to the sheath so as to contract the sheath about the graft, utilising the sheath to position the graft into its site of application, and affixing the graft and sheath into position.
In order to facilitate insertion of the graft into the tube of sheath material, a tubular mesh holder may be provided having a diameter sufficient to allow the graft to pass therethrough. The mesh holder is inserted into one end of the sheath tube and then the graft is passed through the mesh holder and into the sheath.
The sheath of embodiments of the invention allows delivery of a graft held therein to its site of application without attaching sutures or the like to the graft itself, which therefore avoids potential damage to the graft during insertion. The sheath additionally provides a measure of protection to the graft by surrounding the graft during the insertion procedure. If desired, the graft may be maintained under tension during the insertion and attachment procedure by maintaining tension on the ends of the sheath. The sheath is fixed in place together with the graft, and is absorbed, or at least partially absorbed, over a period of time following insertion into the body.
The invention is described in greater detail hereinafter, by way of example only, with reference to the accompanying drawings, wherein: